1. FIELD OF THE INVENTION
The present invention relates to an interrupt control system, and in particular, to an interrupt control system applicable to an error recovery to be conducted in an input/output system having a plurality of access paths.
2. DESCRIPTION OF THE PRIOR ART
Conventionally, in a system in which a plurality of central processing units, CPU's access a plurality of shared units such as input/output units or external storage devices, a shared unit to be accessed by a CPU is connected via a dedicated path to the CPU. If the same CPU desires to access the same shared unit via another path so as to establish a connection therebetween, a Start I/O instruction must be executed. For the execution of the Start I/O instruction, a considerable processing time is required for each instruction. To overcome this difficulty, there has been proposed a system in which a map reflecting the network state is generated and stored in a control unit, and when executing a series of instructions, the control unit disconnects a shared unit from a channel and thereafter connects the disconnected unit to another channel based on the information contained in the map (Japanese Patent Examined Publication No. 58-38818).
FIG. 4 is a schematic diagram illustrating the configuration of an input/output system utilizing the interrupt control method of above-mentioned system.
The system of FIG. 4 comprises disk control units 11-12, channel switches 16-17, string controllers 13-14, a control memory 18, and disk drive units 15 (shared devices #1-#N).
The disk control units 11-12 are each connected to a plurality of channels via the channel switches 16 and 17, respectively, and are also connected to the string controllers 13 and 14, respectively. The string controllers are connected to a plurality of disk drive units 15. The control memory 18 is shared between the string controllers 13 and 14.
In this case, when path #j (j = 1, 2, . . . , m) of the channel switch 16 and path #k (k = 1, 2, . . . , n) of the channel switch 17 are connected to the same CPU, if the state of the channel selection is notified to the disk control units 11 and 12 by use of specific commands, the path #j of the channel switch 16 and the #k of the path channel switch 17 form a path group. The information that the path #j and #k are of the same path group is recorded in the control memory 18 by the disk control unit 11 or 12. In the operation after this point, the disk control units 11-12 check the control memory 18 to confirm the information of the path group.
In FIG. 4, a command chain issued to the device #i (i = 1, 2, . . . , N) of the disk drive unit 15 via the path #j of the channel switch 16 is processed as follows.
(i) First, the disk control unit 11 receives a Seek and Set Sector command via the path #j of the channel switch 16 and directs the instruction of the command to the disk drive unit 15 through the string controller 13. PA0 (ii) The disk control unit 11 records in the control memory 18 the information that the Seek and Set Sector instruction has been issued to the device #i of the disk drive unit 15 through the path group including the path #j of the channel switch 16 and the path #k of the channel switch 17. PA0 (iii) The disk control unit 11 disconnects the linkage between the channel and the string controller 13. In this operation, the linkage to the channel is disconnected by reporting a status code including only "the channel end" information to the channel. The disconnection is recorded in the control memory 18. PA0 (iv) The string controller 14 reports the change in the contents of the control memory 18 to the disk control unit 12. PA0 (v) The disk control unit 12 reads the control memory 18 and recognizes that the Seek and Set Sector command has been specified to the device #i of the disk drive unit 15 through the path group comprising the path #j of the channel switch 16 and the path #k of the channel switch 17. PA0 (vi) On the other hand, when the device #i of the disk drive unit 15 completes the Seek and Set Sector commands initiated according to the operation of step (i) described above, it causes an interrupt to be sent to the string controllers 13-14 to indicate the completion. PA0 (vii) The string controllers 13-14 cause an interrupt to the disk control units 11 and 12, respectively, to report the completion of the operation. PA0 (viii) To report the completion of the path #j of the channel switch 16 or to the path #k of the channel switch 17, the disk control unit 11 issues a request for the reconnection to the channel via the path #j of the channel switch 16. PA0 (ix), Since the disk control unit 12 must also indicate the completion to the path #j of the channel switch 16 or the path #k of the channel switch 17, it issues a request for the reconnection to the channel via the path #k of the channel switch 17. PA0 (xi) Data transfer from the channel to the device #i of the disk drive unit 15 is carried out via the path established in step (x) described above.
In this case, the path #j of the channel switch 16 or the path #k of the channel switch 17 is reconnected. If the path #k of the channel switch 17 is reconnected, a path is established from the path #k of the channel switch 17 via the disk control unit 12 and the string controller 14 to the device #i of the disk drive unit. Since the Seek and Set Sector operation has been completed on the device #i of the disk drive unit 15, the completion is reported through the path #k of the channel switch 17.
In the conventional method, the reconnection has been conducted only by use of the channel switch actuated (the path #j of the channel switch 16 in the system of FIG. 4); however, the control method described above enables the reconnection to be performed via a channel switch belonging to a path group initiated (the path #j of the channel switch 16 or the #k of the channel switch 17 of FIG. 4). In the control method of FIG. 4, therefore, the possibility of successful connections is increased, thereby greatly reducing the number of unsuccessful Set Sector operations which have long remained unsolved. In general, since the linkage to a channel is disconnected by reporting a status only containing "the channel end" only when a simple multioperation is carried out, the function for establishing a reconnection path by use of an arbitrary channel switch in the path group brings forth an advantageous effect.
In the control method, however, a path for which a linkage in the path group has been disconnected may be used again to establish the reconnection path. For example, if an error which has occurred on an activated path is to be recovered by a command retry, the reconnection should not be carried out by use of the activated path. The Japanese Patent Examined Publication No. 58-38818 has not disclosed any ideas applicable to such a case, and hence the error cannot be recovered.